This was during the first mission of a CW expedition. Host crashed, so we migrated to a different one, after which I spawned in with my weapons from adventure mode, and not the base versions you usually start CW off with, which you can see by my Handgun having the red illusion it usually has, while still displaying white item stats.
I could fully utilize the properties of my weapons from Adventure mod too, regardless of what the stats at the top say, as my Spear and Shield had additional stamina, and I could proc Swift Slaying.
After finishing the mission, the weapons reverted back to the ones I had prior to host migration, both visually and mechanically.
The same thing happened during a Citadel mission on a different run, so I guess it’s possible for it to happen at any point Host Migration occurs, regardless of whether or not you already upgraded your weapons, or swapped them out for a random ones.